For use as a clutch part in an automatic transmission of a vehicle, a paper requires superior physical properties including friction and wear properties, durability, and porosity. Particularly, an automatic transmission clutch is required to exhibit excellent hot-temperature friction property, wear resistance, and durability even in an oil-impregnated condition as it works in a transmission oil.
As a wet clutch material, a paper, a sintered copper (Cu), a resin, or graphite has conventionally been used, and the paper has been generally used for a friction material of vehicles.
The paper includes pulp with an inorganic filler and a thermosetting resin (phenol, epoxy, melamine, and the like) added as supplements. Kinds and amounts of the inorganic filler have been known to have great influence on friction properties of the paper.
The matters described as the background arts are only intended to increase the understanding of the background of the present invention, but should not be recognized as being prior arts which are already known to those skilled in the art.